1. Field of the Invention
The present invention relates to video amplifier circuitry for controlling a signal to be displayed on a display device such as a cathode ray tube (CRT), and in particular, to video circuitry for controlling signal gain and reference block level of a video signal.
2. Description of the Related Art
Video display devices are used for many purposes, including video monitors for displaying video images generated by computers and televisions for displaying animated or live action video images such as those received over cable or broadcast systems. One of the more common types of video display devices uses a cathode ray tube (CRT) to display the video image information. As is well known, the CRT includes three primary color cathode ray guns which are manipulated to converge on a screen and produce a color image. The three ray guns produce converged scaning rasters having red, green and blue fields which combine to produce all colors from black through white. For manufacturers of such display devices, one important requirement is that of establishing and maintaining color balance by appropriately balancing the signals driving the red, green and blue (RGB) cathodes of the CRT. This is generally quite difficult since adjusting independent video gain stages for each channel (red, green, and blue) often conflicts with establishing and maintaining proper reference black level, or brightness, adjustment for each channel.